In many medical and operative procedures, it is necessary to hold a patient's head in a particular position. For example, a patient's head is held stationary while a fracture or dislocation of the cervical spine is healing. Typical structures for performing that function are conventional halos, and cervical traction rings, such as shown in U.S. Pat. Nos. 4,475,550 and 4,612,930, the disclosures of which are hereby incorporated by reference herein.
Conventional skull pins which are utilized with halos and cervical traction rings sometimes do not hold in the skull bone as securely as desired. There is sometimes a tendency for the pins to pull out when subjected to sideways (e.g. shear) forces. Therefore it is desirable to provide a more secure fixation for skull pins than has traditionally been provided.
Conventional skull pins also are typically made of medical grade stainless steel. Such pins have the drawback, however, of artifacting much more than bone when subjected to an imaging procedure. If the pins are made of titanium, which does not artifact nearly as much as stainless steel, then the tips have a tendency to break off as a result of shear forces. If this skull engaging portions of the pins are made out of biologically compatible ceramic material, such as shown in said U.S. Pat. No. 4,612,930, again there is the possibility that the tips will break off since the material is relatively brittle.
There have been experimental pins tested, such as described in a 1986 article in Spine Medical Journal, at pages 977 through 981, which seek to improve halo skull pin design by making the fixation more secure (providing shear resistance), while enhancing penetration prevention. Such experimental pins, however, are not practical since under cyclical loading the skull bone will wear or erode, and such experimental pins are not capable of being advanced so as to always be properly engaging the bone to accommodate wear or erosion.
According to the present invention, a skull pin is provided which is an improvement over both conventional skull pins-- having enhanced shear resistance, and fixation to the skull and allowing them to be made of a wider variety of materials-- and the experimental pins discussed above, and capable of being retightened if the skull bone is subjected to wear or erosion.
The skull pin according to the present invention has a design which allows the tip thereof to hold more securely in the skull when subjected to sideways forces, and to be made out of a more brittle material than has been practically utilized in the past, typically a material that does not significantly artifact, such as titanium, or a material that does not artifact significantly more than bone, such as biologically compatible ceramic (single crystal alumina ceramic), or a gem stone (e.g., sapphire).
According to one aspect of the present invention, a skull pin is provided having a main cylindrical body portion, and a skull engaging portion. The skull engaging portion comprises first and second concentric, in-line cylinders terminating in conical sections, the first conical section terminating in the second cylinder, and the second conical section terminating in a pointed tip. While the dimensions may vary for a number of reasons, it is preferred that the cylinders be circular in cross section, with the first cylinder having a diameter of about 0.18 in.; the first conical section a length of about 0.09 in. and approximately a 60.degree. taper; the second cylinder having a length of about 0.03 in. (e.g., about 1/32 of an inch) and a diameter of about 0.07 in.; and the second conical section having approximately a 60.degree. taper. The skull pin, particularly, the skull engaging tip portion thereof, may be made from medical grade stainless steel, but preferably is made of titanium, biologically compatible ceramic, a gem stone, or a like material that does not significantly artifact. The skull pin is typically used in combination with a halo or cervical traction ring, as is conventional.
According to another aspect of the present invention, a skull pin is provided having a skull engaging portion thereof made of material which does not artifact significantly. The skull engaging portion is a pointed tip termination, a sideways (shear) force resisting, fixation enhancing section (e.g., a short cylindrical section having a length approximately equal to or slightly less than the thickness of the outer table of a human skull) adjacent the pointed tip to minimize the probability that the tip will be snapped off, and a conical section for facilitating tight adjustment of the pin to a human skull if the skull wears or erodes as a result of cyclical loading.
According to another aspect of the present invention, a skull pin is provided comprising: A main substantially cylindrical body elongated in a dimension of elongation, and having first and second ends. A skull engaging portion connected to the main body and extending outwardly from the first end thereof in the dimension of elongation. A stepped tip portion of the skull engaging portion, the stepped tip portion remote from the main body, and having: a first conical section closest to the cylinder first end, the first conical section having a diameter tapering from its largest extent to its smallest extent moving away from said main body in said dimension of elongation, and at its largest area less than the largest cross-sectional dimension of the main cylindrical body; the first conical section terminating in a short cylindrical section extending outwardly from the first conical section in the dimension of elongation, the short cylindrical section having a largest cross-sectional dimension which is much smaller than the largest cross-sectional dimension of the main body; and the short cylindrical section terminating at an end thereof most remote from the main body in a second conical section, which itself terminates in a pointed tip at an end thereof most remote from the main body. The main body is circular in cross section and exteriorly threaded.
It is a primary object of the present invention to provide an improved skull pin, capable of better resisting shear forces, enhancing fixation, while still facilitating tight adjustment in a skull even if the skull wears or erodes as a result of cyclical loading, and allowing a wide variety of different materials to be used in construction, which materials may be chosen so that they do not significantly artifact. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.